1. Field of Invention
This invention generally relates to imaging members for electrophotography.
2. Description of Related Art
In electrophotography, an electrophotographic substrate containing a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging a surface of the substrate. The substrate is then exposed to a pattern of activating electromagnetic radiation, such as, for example, light. The light or other electromagnetic radiation selectively dissipates the charge in illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in non-illuminated areas of the photoconductive insulating layer. This electrostatic latent image is then developed to form a visible image by depositing finely divided electroscopic marking particles on the surface of the photoconductive insulating layer. The resulting visible image is then transferred from the electrophotographic substrate to a necessary member, such as, for example, an intermediate transfer member or a print substrate, such as paper. This image developing process can be repeated as many times as necessary with reusable photoconductive insulating layers.
Electrophotographic imaging members (i.e. photoreceptors) are well known. Electrophotographic imaging members are commonly used in electrophotographic (xerographic) processes having either a flexible belt or a rigid drum configuration. These electrophotographic imaging members sometimes comprise a photoconductive layer including a single layer or composite layers. These electrophotographic imaging members take many different forms. For example, layered photoresponsive imaging members are known in the art. U.S. Pat. No. 4,265,990 describes a layered photoreceptor having separate photogenerating and charge transport layers. The photogenerating layer disclosed in the 990 patent is capable of photogenerating holes and injecting the photogenerated holes into the charge transport layer. Thus, in the photoreceptors of the 990 patent, the photogenerating material generates electrons and holes when subjected to light.
More advanced photoconductive photoreceptors containing highly specialized component layers are also known. For example, a multilayered photoreceptor employed in electrophotographic imaging systems sometimes includes one or more of a substrate, an undercoating layer, an intermediate layer, an optional hole or charge blocking layer, a charge generating layer (including a photogenerating material in a binder) over an undercoating layer and/or a blocking layer, and a charge transport layer (including a charge transport material in a binder). Additional layers such as one or more overcoating layer or layers are also sometimes included.
U.S. Pat. No. 5,958,638 discloses some known materials used for undercoating layers. Materials known to be usable in intermediate and undercoating layers include a resin material alone, such as polyethylene, polypropylene, polystyrene, acrylic resin, vinyl chloride resin, vinyl acetate resin, polyurethane, epoxy resin, polyester, melamine resin, silicone resin, polyvinyl butyryl, polyamide and copolymers containing two or more of repeated units of these resins. Such resin materials also include casein, gelatin, polyvinyl alcohol, ethyl cellulose, etc. Intermediate and undercoating layers are typically formed by a dip coating process, such as the methods disclosed in, for example, U.S. Pat. Nos. 5,958,638 and 5,891,594.
U.S. Pat. No. 5,471,313 discloses a xerographic device having a laser power controller that includes a setup routine. The setup routine disclosed in the 313 patent determines a relationship between an initial charge on a photoreceptor Vhi and an exposed voltage, Vlow, as a function of a laser power setting. The setup routine disclosed in the 313 patent stores these relationships as curves on a graph. These curves provide an initial estimate of the required laser power. A feedback laser power controller takes an initial charge level, Vhi, and a discharge ratio, DR, and determines an appropriate discharge level from the setup data. The controller measures the exposed voltage, Vlow, on the photoreceptor and adjusts the laser power to convert for changing photoreceptor properties. The discharge ratio, DR, is equal to the ratio (Vlow−Vres)/(Vhi−Vres), where Vres equals a baseline voltage, measured by exercising the laser power exposure until the exposed voltage does not discharge further with increasing exposure power. The discharge ratio indicates where a development potential, Vdev, and a cleaning potential, Vclean, are positioned on a photo-induced discharge curve, where Vclean is a cleaning potential equal to the difference between a housing bias voltage and the voltage of areas discharged by exposure. The expression “photo-induced discharge curve” (PIDC), as used here, refers to a relationship between the potential as a function of exposure and a measure of the sensitivity of the device. The photo-induced discharge curve generally represents the supply efficiency i.e., the number carriers injected from the generator layer into the transport layer per incident photon, as a function of the field across the device.
U.S. Pat. No. 5,797,064 discloses a pseudo photo-induced discharge curve setup procedure for a xerographic system. The procedure disclosed in the 064 patent does not use an electrostatic voltmeter (ESV). Rather, the procedure for the 064 patent determines the location of a knee of the pseudo photo-induced discharge curve, in response to charging a photoreceptor or raster output scanner (ROS).